A major group of proteolytic enzymes present in the cell are the sulfhydryl proteases. These enzymes include the lysosomal proteases Cathepsins B1, B2 and C. The primary objective of research in our laboratory is the development of simple isolation procedures for Cathepsins B1 and B2, their characterization, investigation of their active sites, mechanism of action and amino acid sequence. It is hoped that these studies will help to elucidate the role of sulfhydryl proteases in the intracellular protein turnover.